(1) Field of the Invention
This invention relates generally to communications and, more particularly, to packet communications systems.
(2) Background Art
As the Internet evolves, a variety of new services have been defined for Internet Protocol (IP) based technology. These include xe2x80x9cIntegrated servicesxe2x80x9d (such as controlled load service and guaranteed service) and xe2x80x9cdifferentiated services.xe2x80x9d Based on these services, an IP-based network is able to carry multimedia traffic, including voice, data and video, within various performance requirements.
Unfortunately, the very size of the underlying packet payload of some multimedia traffic may cause performance problems. In particular, voice packets are in general quite small. ITU-T G723.1 specifies generation of a 20 byte speech packet at 30 ms intervals (e.g., see ITU-T Recommendation G.723.1 xe2x80x9cDual Rate Speech Coder for Multimedia Communications Transmitting At 5.3 and 6.3 Kbps,xe2x80x9d 1995). Consequently, packets used to transport voice are subjected to a large overhead. For example a 20-byte voice packet transmitted using a User Datagram Protocol/Internet Protocol (UDP/IP) encapsulation incurs an overhead of 28 bytes (20 byte IP header, plus up to 8 bytes of UDP header), or 140%. If using Real Time Protocol (RTP)/UDP/IP encapsulation, the overhead is 40 bytes (12+8+20), or 200%. In addition, if each application session (also referred to herein as an audio stream, or packet flow, or call), requires use of one UDP port number, the resulting large number of packets may create heavy packet processing load for any intermediate routers and available. Further, there are a finite number of UDP port numbers, which may also be a limiting factor on the available number of sessions.
As such, various multiplexing schemes have been proposed to address the bandwidth efficiency problem caused by small payloads carried by packets with relatively large headers over an IP-based network (e.g., see J. Rosenberg, xe2x80x9cAn RTP Payload Format for User Multiplexing,xe2x80x9d work in progress, drafi-ietf-avt-aggregation-00.txt; and B. Subbiah, S. Sengodan, xe2x80x9cUser Multiplexing in RTP payload between IP Telephony Gateway,xe2x80x9d work in progress, draft-ietf-avt-mux-rtp-00.txt, August 1998; the co-pending, commonly assigned, U.S. Patent application of Chuah et al. entitled xe2x80x9cA Lightweight Internet Protocol Encapsulation (LIPE) Scheme for Multimedia Traffic Transport,xe2x80x9d application Ser. No. 09/264,053, filed on Mar. 9, 1999). These schemes propose different. ways to multiplex multimedia traffic (e.g., voice packets) from different, calls using a single multiplexing session using IP-based encapsulation (an RTP/UDP/IP session in the former two articles, or a UDP/IP session in the latter patent application) between two packet endpoints of an IP network.
These multiplexing schemes are efficient when large numbers of application sessions originate and terminate between the same pair of packet endpoints (or IP interfaces). However, if traffic dispersion occurs, there may be a decrease in multiplexing efficiency. In particular, when different pairs of packet endpoints are involved, the number of application sessions multiplexed into a particular multiplexing session may decrease and therefore result in the degradation of multiplexing efficiency. This is observable from FIG. 1, which illustrates the use of an IP-based network 120 to provide transport between a number of wireless base stations (105, 110, and 115) and a number of frame selector units (FSUs 140 and 145) as known in the art. The solid lines between these packet endpoints and the IP-based network 120 are representative of well-known communications facilities. A base station (BS) (105, 110, and 115) may handle calls that go to any one of a number of FSUs (as illustrated by FSUs 140 and 145). This is shown for BS 110, which sources traffic that must be split into two multiplexed sessions 111 and 112 (dotted lines) between FSUs 140 and 145, respectively. Consequently, not much multiplexing gain can be achieved by using multiplexing session 111 between BS 110 and FSU 140. This is also illustrated in FIG. 2, which shows a corresponding view of the two multiplexed UDP/IP application sessions using the above-mentioned LIPE. In this context, assume that BS 110 handles calls 1, 2, 3, and 4 and that calls 1 and 3 are destined for FSU 140 and that calls 2 and 4 are destined for FSU 145. This requires two multiplexed UDP/IP application sessions: 150 and 155. Application session 150 multiplexes payloads for calls 1 and 3, while application session 155 multiplexes payloads for calls 2 and 4. Similarly, an FSU may be sourcing traffic that is split among different multiplexed sessions to the BSs (e.g., 105, 110, and 115) and be similarly underutilized.
An application level switching server is used within an IP-based network to counter any multiplexing gain, loss due to traffic dispersion. The application level switching server receives a stream of mini-packets encapsulated within a larger Internet Protocol based (IP) packet, where the larger IP based packet is associated with a first multiplexed session and each mini-packet is associated with a particular application session. In accordance with the invention, the application level switching server routes each received mini-packet as a function of routing information that associates header information from each received mini-packet with another multiplexed session such that mini-packets within a multiplexed session can be routed to different multiplexed sessions. As a result, application sessions associated with the first multiplexed session are re-packed into other multiplexed sessions.
In an embodiment of the invention, an IP-based network incorporates an application level switching server and a number of packet endpoints. A packet endpoint multiplexes application sessions destined for different packet endpoints into one multiplexed session that is terminated with the application level switching server. The latter extracts each application session (or packets associated therewith) and repackages, or switches, them into other multiplexed sessions such that switched packets are transmitted to different packet endpoints. The multiplexed sessions utilize either RTP/UDP/IP or UDP/IP encapsulation.